In association with development of a network technology, a way of shopping has been changing. Specifically, a form of directly going to a shop to purchase a product has been transitioned to a form of purchasing a product at home via a communications network such as the Internet. For a company that sells products, to sell the company's products, the products need to catch many people's attention as much as possible. Conventionally, for example, by increasing advertisements by commercial and new shops, the purpose has been partially achieved. However, in association with the above-described change, an effect of attracting people's attention to the products on the communications network has been outstanding. Under such circumstances, for example, Patent Literature 1 has proposed an efficient creation of a product listing by a product introducer. Accordingly, a large number of product introducers list identical products and introduce the products via the communications network. That is, the products come under the public via the communications network, promoting the sales of the products.